The present invention relates to a rod-shaped high-stress active connection element for connecting at least two structural components as well as to a rotorcraft, particularly a helicopter, having at least one such connection element.
From German Patent Documents DE 198 13 959 A1, DE 101 39 686 A1 as well as DE 101 54 391 A1 respectively, a rod-shaped high-stress active connection element is known for connecting at least two structural components. Such active connection elements, which are also called active struts, are used particularly in the case of rotorcraft or helicopters in order to mutually connect at least a first structural component (such as a transmission) and at least a second structural component (such as an airframe) in a secure manner and actively suppress or minimize vibrations, particularly structure-borne noise, and to insulate the second structural component as much as possible with respect to the latter. A corresponding connection element has to transmit loads of several tons and is a safety-relevant component. Such connection elements are becoming increasingly important in rotorcraft technology, because the impairment of the passenger comfort as well as structural stress caused by sound and vibrations are still very high, and an improvement can be achieved by means of these components.
Such a connection element comprises a first end with a first connection area, which is assigned to the first structural component, and a second end with a second connection area, which is assigned to the second structural component; a load-diminishing intermediate section arranged between the first and second connection area, through which intermediate section the flux of force between the first and second connection area extends when the connection element is loaded; at least one controllable extension actuator having a piezo stack or a flat piezo arrangement, which extension actuator is arranged parallel to the intermediate section and, when operated, extends the connection element at least in the area of the intermediate section in a controlled manner in order to actively suppress or insulate vibrations between the first and second structural component; a prestressing device having a prestressing element exercising a mechanical pressure-type prestressing onto the piezo stack.
In the case of the connection elements of the above-mentioned type, the connection areas are constructed in the form of a continuous strut or a continuous rod in one piece with the intermediate piece. Extension actuators with a flat piezo arrangement are normally glued directly onto the outer circumference of the strut. Extension actuators with a piezo stack, in turn, are mounted by special separate external holding devices, which are fastened to the strut, on the exterior side of the strut. When such a separate holding device is used, the prestressing device arranged parallel to the intermediate section is fixed on this holding device. In particular, in the case of extension actuators with a flat piezo arrangement, a prestressing is achieved in that the carrier structure to which the extension actuator is applied, is first subjected to a tensile stress and is then relaxed again after the mounting of the piezo stack.
Arrangements are also known in which the extension actuator is arranged in series with the intermediate section. However, such configurations have been less successful in practice and are therefore of secondary importance.
The above-mentioned known constructions have various disadvantages. Thus, it was found that, in particular, glued-on extension actuators with flat piezo arrangements chip off easily in the operation of the strut and therefore fail. Such extension actuators also only have a fairly low efficiency and can transmit only comparatively low forces to the strut. Piezo stacks, which per se have a higher efficiency than completely flat piezo arrangements, cannot be used in this type of actuator.
Although in the case of connection elements or struts equipped with separate holding devices and prestressing devices, the use of extension actuators having a piezo stack can be implemented, these conventional constructions require very high expenditures with respect to their construction and manufacturing and are also relatively heavy, which does not meet the light-weight construction requirements existing in aircraft construction. Furthermore, the mounting of separate holding devices and prestressing devices on the exterior side of the strut as well as the establishment of a secure connection between these components presents problems because, on the one hand, a good connection of the holding device with respect to the strut has to exist in order to introduce the forces of the actuator into the strut but, on the other hand, the strut should not be weakened by stress concentration, unfavorable stiffness skips, and the like.
Also in the case of such connection elements or struts, it was found that the efficiency of the extension actuator is not optimal. For an improvement of the efficiency, the stiffnesses of the participating structural components have to be mutually matched and adapted in a specific manner. However, in the case of these types of constructions, this would again result in an excessively reduced diameter and thus to a weakening of the strut. As a result, no more favorable solution could be implemented in this type of construction.
In the case of the above-described known connection elements, it is difficult to electrically insulate the extension actuators, which are operated electrically because of the used piezo technology, from the connection element or the strut, particularly because, as a rule, so far the struts have been constructed of a metallic material.
From German Patent Documents DE 196 53 555 A1, DE 199 06 468 A1 and DE 39 22 504 A1, controllable extension actuators are known which comprise a housing body and a piezo stack arranged inside the housing, which piezo stack is functionally coupled with a control element of the extension actuator. Furthermore, a prestressing element is arranged inside the housing, which prestressing element exercises a mechanical pressure-type prestressing on the piezo stack. This prestressing element is, for example, a compression spring or bellows which encloses the piezo stack. By way of intermediate elements, such as intermediate disks, the prestressing element is supported on the housing and the piezo stack. German Patent Document DE 39 22 504 A1 also discloses a variant, in the case of which the prestressing element in the form of bellows is arranged inside a passage opening provided in the piezo stack.
German Patent Document DE 42 28 974 A1 shows a comparable extension actuator, in the case of which the prestressing element in the form of a cup spring is arranged outside the actual housing between an external housing section and a tappet projecting out of the housing. Such extension actuators are normally used for the operation of an injection nozzle or a comparable function element. In contrast to the above-mentioned load-diminishing active connection elements, the extension actuators or their housings have no special load-diminishing functions and are also not used for manipulating their own housing for the purpose of a vibration insulation or reduction. Extension actuators of the type mentioned in this and the preceding section are therefore also not the object of the present invention.
The invention is based on the object or on the technical problem of creating a rod-shaped high-stress active connection element of the above-mentioned type which avoids as much as possible the disadvantages of the prior art and, without impairing its functionality and safety with respect to its vibration insulating and minimizing characteristics, has an improved efficiency. In addition, a rotorcraft, particularly a helicopter, is to be provided which has at least one such connection element.
According to a first aspect, this object is achieved by means of a rod-shaped high-stress active connection element for connecting at least two structural components, the connection element comprising;
a first end with a first connection area which is assigned to the first structural component, and a second end with a second connection area which is assigned to the second structural component;
a load-diminishing, mechanically highly stressable intermediate section which is arranged between the first and the second connection area and through which the flux of force between the first and second connection area extends when the connection element is stressed;
at least one controllable extension actuator which has at least one piezo stack and is arranged parallel to the intermediate section and, when operated, extends the connection element in a controlled manner at least in the area of the intermediate section in order to actively suppress or insulate vibrations between the first and second structural component; and
a prestressing device with a prestressing element, which exercises a mechanical pressure-type prestressing onto the piezo stack. The connection element according to the invention which may be further developed, for example, in the form of an oblong or more compact strut or the like, is characterized in that the prestressing element is the load-diminishing intermediate section itself.
The connection element according to the invention or its extension actuator can be controlled by a controlling and/or regulating device known per se, which comprises at least one vibration sensor which may be arranged, for example, in the vicinity of at least one of the connection areas or on at least one of the structural components to be connected.
In the case of the connection element according to the invention, the intermediate section does not only take over a purely load-diminishing function but simultaneously also the function of a highly effective prestressing element by means of which high prestressing forces can be transmitted to the piezo stack. In this case, the prestressing takes place in the longitudinal direction of the connection element or essentially in the longitudinal direction of the connection element and is selected such that the piezo stack is never relieved or even subject to tensile loading during the operation of the connection element and possibly destroyed thereby. The used piezo elements can be stacked in the longitudinal direction of the connection element and over essentially the entire length of the intermediate section. This results in a large stacking height and thereby already in a greater implementable actuating movement than in the case of extension actuators with a flat arrangement of piezo elements.
Separate holding devices to be mounted on the outside on the prestressing elements and prestressing devices for the piezo elements, as they are known from the prior art, are not necessary for the solution according to the invention. The disadvantages occurring in the known constructions, such as the problematic mounting of the holding device or prestressing device on the intermediate piece, undesirable stress concentrations, stiffness skips, insufficient prestressing forces or the like, can be effectively avoided. Furthermore, the construction of the connection element according to the invention and of the extension actuator is simplified, and the overall weight of the connection element is reduced. Also in comparison to known pure extension actuators, which take over no load-diminishing function, a simplification of the construction can be achieved since, in the solution according to the invention, the load-diminishing intermediate section takes over an advantageous multiple function and thus additional separate prestressing elements, which have to be mounted firmly to the connection element, can be eliminated.
Although the connection element according to the invention is stressed by the prestressing of the piezo stack in addition to the loads already existing as a result of the connection between the at least two structural components, it can absorb this loading without any problem and always securely connect the at least two structural components because the connection element according to the invention is essentially loaded only by longitudinal forces, which permits a simple dimensioning and mechanically favorable conditions while the weight is low. Because of the construction according to the invention, a reliable load transmission is naturally also ensured in the event that the extension actuator fails.
Furthermore, in the case of the connection element according to the invention, the extension actuator has a higher efficiency. This is a result of the improved prestressing of the piezo stack by the load-diminishing connection element itself and of an optimized stiffness ratio of the intermediate section and the piezo stack. For achieving this suitable stiffness ratio, it is not required to provide the connection element with an unfavorable diameter and to thereby weaken it. The parameters and rules required for the optimization will be more precisely described in the following.
Because of the high efficiency, comparatively high forces and large actuating movements can be transmitted to the intermediate section by means of the extension actuator in the operation of the active connection element according to the invention, whereby an improved vibration insulating and minimizing behavior can be implemented.
The connection element according to the invention with its piezo extension actuator is therefore a highly effective and reliable multifunction component which, in addition to having a pure connecting and load-diminishing function, particularly when used in rotorcraft, contributes to a considerable reduction of the vibrations transmitted to an airframe and thus to an improvement of the passenger comfort and to a reduction of vibration-caused loads upon the structure.
Additional preferred and advantageous design characteristics of the connection element include the following.
According to a second aspect, the object of the invention is achieved by a rotorcraft according to the invention, particularly a helicopter, having at least a first structural component (such as a transmission) and at least a second structural component (such as a helicopter airframe) which are connected with one another by at least one active connection element according to the present invention. The rotorcraft according to the invention essentially has the same advantages as those explained above in connection with the connection element according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.